JBoss Drools: Reasoning on QuickFIX-J data model

I just tried to make a simple JBoss Drools example which could probably handle QuickFIX-J messages. So I created the simplest rule flow, including one RuleSet node, mapped onto a ruleflow-group in a DRL file.


same in textual form:

<?xml version="1.0" encoding="UTF-8"?> 
<process xmlns="http://drools.org/drools-5.0/process"
         xmlns:xs="http://www.w3.org/2001/XMLSchema-instance"
         xs:schemaLocation="http://drools.org/drools-5.0/process drools-processes-5.0.xsd"
         type="RuleFlow" name="oms" id="my.oms" package-name="my.oms" >

  <header>
  </header>

  <nodes>
    <start id="1" name="Start" x="16" y="16" width="80" height="40" />
    <actionNode id="2" name="Action" x="128" y="16" width="80" height="40" >
        <action type="expression" dialect="java" >System.out.println("Action Start");</action>
    </actionNode>
    <ruleSet id="3" name="RuleSet" x="240" y="16" width="80" height="40" ruleFlowGroup="my-oms" />
    <actionNode id="4" name="Action" x="352" y="16" width="80" height="40" >
        <action type="expression" dialect="java" >System.out.println("Action End");</action>
    </actionNode>
    <end id="5" name="End" x="464" y="16" width="80" height="40" />
  </nodes>

  <connections>
    <connection from="1" to="2" />
    <connection from="2" to="3" />
    <connection from="3" to="4" />
    <connection from="4" to="5" />
  </connections>

</process>

Next describe to rule in a DRL file:

package my.oms

import quickfix.fix44.NewOrderSingle
import quickfix.field.MinQty

rule "reset minqty"
dialect "mvel" 
ruleflow-group "my-oms"
  when
    $order : NewOrderSingle($qty : minQty)
    MinQty(value == 1.0 || value > 100.0) from $qty
  then
    System.out.println("reset order: " + $order); 
    modify($order){
      $order.set(new MinQty(20));
    }
end

What looks a little strange to me is the when part:

    $order : NewOrderSingle($qty : minQty)
    MinQty(value == 1.0 || value > 100.0) from $qty

I spent just quite a few minutes to figure out why my first version of the rule didn't work as I expected. It seemed to me that it would be more natural to make it just in one line, something like this:

  NewOrderSingle(MinQty(value == 1.0 || value > 100.0))

With a Java code from the Drools examples (which may also are generated when you create a Drools Project with the Drools eclipse plug-in), I run the example and it works fine.

package my.oms;

import org.drools.KnowledgeBase;
import org.drools.KnowledgeBaseFactory;
import org.drools.builder.*;
import org.drools.io.ResourceFactory;
import org.drools.logger.KnowledgeRuntimeLogger;
import org.drools.logger.KnowledgeRuntimeLoggerFactory;
import org.drools.runtime.StatefulKnowledgeSession;

import quickfix.field.MinQty;
import quickfix.fix44.NewOrderSingle;


public class MyOms {

 public static final void main(String[] args) {
  try {
   // load up the knowledge base
   KnowledgeBase kbase = readKnowledgeBase();
   StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession();
   KnowledgeRuntimeLogger logger = KnowledgeRuntimeLoggerFactory.newFileLogger(ksession, "test");
   // go !
   
   NewOrderSingle order = new NewOrderSingle();
   order.set(new MinQty(1.0));
   
   NewOrderSingle order1 = new NewOrderSingle();
   order1.set(new MinQty(111.0));
   
   NewOrderSingle order2 = new NewOrderSingle();
   order2.set(new MinQty(222.0));
   
   ksession.insert(order);
   ksession.insert(order1);
   ksession.insert(order2);
   ksession.startProcess("my.oms");
   ksession.fireAllRules();
   
   logger.close();
  } catch (Throwable t) {
   t.printStackTrace();
  }
 }

 private static KnowledgeBase readKnowledgeBase() throws Exception {
  KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
  kbuilder.add(ResourceFactory.newClassPathResource("oms.drl"), ResourceType.DRL);
  kbuilder.add(ResourceFactory.newClassPathResource("oms.rf"), ResourceType.DRF);
  KnowledgeBuilderErrors errors = kbuilder.getErrors();
  if (errors.size() > 0) {
   for (KnowledgeBuilderError error: errors) {
    System.err.println(error);
   }
   throw new IllegalArgumentException("Could not parse knowledge.");
  }
  KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();
  kbase.addKnowledgePackages(kbuilder.getKnowledgePackages());
  return kbase;
 }
 
}

This example just shows that with Drools one may handle even quite complex data model, such as QuickFIX-J's one. Next, it would have real value if I'm able to make do the same via Guvnor.

Comparing Strings in C: Wii hack

I've just read an article about game console hacking: Console Hacking 2008: Wii Fail.
One interesting code fragment that was acquired in binary decompilation process:

strncmp(SHA1_sig, SHA1_in, 20);

SHA1_sig, SHA1_in are actually binaries, but are compared like strings, and if both of them start with \0 the strncmp will say that they are equal even if everything else is different.
(As I'm not a C expert to believe it right away) I made a simple code fragment to see it myself:

#include 
#include 

int main(){
  char* x;
  char* y;
  int res;

  x = "\0hello";
  y = "\0bye";

  res = strncmp(x, y, 20);

  printf("The C strings %s and %s are ", x, y);
  if (res == 0){
    printf("equal\n");
  } else {
    printf("not equal\n");
  }
  return 0;
}

So the result will be:

$> ant@ubuntu:~$ gcc test.c ; ./a.out
The C strings  and  are equal

So ... happy hacking! :)

java.lang.System#getenv(String)

java.lang.System#getenv method was deprecated in Java 1.4:

public static String getenv(String name) {
throw new Error("getenv no longer supported, use properties and -D instead: " + name);
}

I would expect this method to be disappeared in Java 5, but due to the huge number of requests, the method was re-implemented again: bug4199068
This is a little strange because if the API was deprecated, you would expect this part to be removed in the next major version. But here, we can see the community influence to the technology :)

SpringSource + Adobe = SpringFramework + Flex

Late in 2008 SpringSource, the SpringFramework vendor, and Adobe, the father of Flex, have partnered to deliver rich Internet applications to Java developers via integration between Spring and Adobe’s Flex.
It was announced that

with support from Adobe, SpringSource is introducing Spring BlazeDS Integration

And just in a few weeks an M1 version for BlazeDS integration was public. This is exactly what I need for my current project, and I can use now an available component, without recreating the wheel :)

Spring, Adobe Partner for Java RIA
Adobe and SpringSource Promise Enhanced Flash-Java Integration
Using BlazeDS with Spring

AOP for Workfow Orchestration

At InfoQ, Oleg Zhurakousky from SpringSource has published an article about Workflow Orchestration Using Spring AOP and AspectJ. The article describes what is needed to implement a flow-like process, to make it flexible and configurable using AOP techniques. I would suggest this article to everyone who is dealing with data flow orchestration and batch processing at work.

Process is a collection of coordinated activities that lead to accomplishing a set goal

Oleg distinguishes the following attributes in his description:

• Activities - activities defining this process


• Shared data/context - defines mechanism to share data and facts accomplished by the activities


• Transition rule - defines which activity comes next after the end of previous activity, based on the registered facts


• Execution Decision - defines mechanism to enforce Transition rule


• Initial data/context (optional) - initial state of the shared data to be operated on by this process

This is actually very similar from what we experienced in designing batch processes using SpringFramework at Swedbank.
I'm happy to see that what we did looks very similar to the example from the article.